RFC 4253 says about the key exchange: > Each side MAY guess which algorithm the other side is using, and MAY send an initial key exchange packet according to t

RFC 4253 says about the key exchange: > Each side MAY guess which algorithm the other side is using, and MAY send an initial key exchange packet according to the algorithm, if appropriate for the preferred method. If you only support one method, that guess will always be correct, and you save a round trip.